Amid weak sales and falling earnings, Target cuts its forecast and announces that 70 million customer accounts have been hacked.

Sales have been weak. Earnings are falling. And the data breach story that erupted last month when Target (Ticker: TGT) revealed that hackers had stolen credit card data for 40 million customers has just gotten a whole lot uglier.

Early Friday, Target announced that up to 70 million customers had personal information – names, addresses and phone numbers – stolen in the same...